Motion Detection Using Pressure Sensing

ABSTRACT

According to an embodiment, a method of sensing motion includes receiving a first signal from a first pressure sensor and a second signal from a second pressure sensor, comparing the first signal and the second signal, and characterizing a motion based on the comparing.

TECHNICAL FIELD

The present invention relates generally to pressure sensing, and, inparticular embodiments, to a system and method for motion detectionusing pressure sensing.

BACKGROUND

Transducers that convert signals from one domain to another are oftenused in sensors. A common sensor that includes a transducer is apressure sensor that converts pressure differences and/or pressurechanges to electrical signals. Pressure sensors have numerousapplications including, for example, atmospheric pressure sensing,altitude sensing, and weather monitoring.

Microelectromechanical system (MEMS) based sensors include a family oftransducers produced using micromachining techniques. MEMS, such as aMEMS pressure sensor, gather information from the environment bymeasuring the change of physical state in the transducer andtransferring the signal to be processed by the electronics, which areconnected to the MEMS sensor. MEMS devices may be manufactured usingmicromachining fabrication techniques similar to those used forintegrated circuits.

MEMS devices may be designed to function as oscillators, resonators,accelerometers, gyroscopes, pressure sensors, microphones, and/ormicro-mirrors, for example. Many MEMS devices use capacitive sensingtechniques for transducing the physical phenomenon into electricalsignals. In such applications, the capacitance change in the sensor isconverted to a voltage signal using interface circuits.

Pressure sensors may also be implemented as capacitive MEMS devices thatinclude a sealed volume and a deflectable membrane. A pressuredifference between the sealed volume and an external volume, such as theambient environment in some cases, causes the membrane to deflect.Generally, the deflection of the membrane causes a change in distancebetween the membrane and a sensing electrode, thereby changing thecapacitance.

SUMMARY

According to an embodiment, a method of sensing motion includesreceiving a first signal from a first pressure sensor and a secondsignal from a second pressure sensor, comparing the first signal and thesecond signal, and characterizing a motion based on the comparing.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a perspective view of an embodiment motion sensor;

FIG. 2 illustrates a waveform diagram of example motion detectionsignals in an embodiment motion sensor;

FIG. 3 illustrates a functional block diagram of an embodiment motionsensor system;

FIG. 4 illustrates a system block diagram of an embodiment motion sensorsystem;

FIG. 5 illustrates a perspective view of an embodiment pressure sensorstructure including an embodiment sensor to air interface;

FIG. 6 illustrates a side view of another embodiment motion sensor;

FIG. 7 illustrates a side view of a further embodiment motion sensor;

FIG. 8 illustrates a cross-sectional view of an embodiment pressuresensor structure;

FIG. 9 illustrates a cross-sectional view of another embodiment pressuresensor structure;

FIGS. 10 a and 10 b illustrate a cross-sectional view and a top view,respectively, of a further embodiment pressure sensor structure;

FIG. 11 illustrates a block diagram of an embodiment method of sensingmotion;

FIG. 12 illustrates a block diagram of another embodiment method ofsensing motion; and

FIG. 13 illustrates a system block diagram of an embodiment MEMSmicrophone system.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of various embodiments are discussed in detailbelow. It should be appreciated, however, that the various embodimentsdescribed herein are applicable in a wide variety of specific contexts.The specific embodiments discussed are merely illustrative of specificways to make and use various embodiments, and should not be construed ina limited scope.

Description is made with respect to various embodiments in a specificcontext, namely motion sensing, and more particularly, motion sensingusing pressure sensors. Some of the various embodiments described hereininclude MEMS transducer systems, MEMS microphone systems, static anddynamic pressure sensors, and motion sensing along multiple axes usingmultiple pressure sensors. In other embodiments, aspects may also beapplied to other applications involving any type of sensor or transducerfor detecting any kind of motion or pressure change according to anyfashion as known in the art.

Motion detection is prevalent in electronic systems with accelerometersand gyroscopes being used in countless systems to provide such motiondetection. For example, automobiles use accelerometers to sense rapidaccelerations or decelerations to trigger air bags; cell phones andtablet computers use accelerometers and gyroscopes to determine phoneposition and align the screen orientation, to control games, and togenerally enable additional functionality; and numerous otherapplications including electronic toys, video game controllers andsystems, computer peripherals, assorted devices, and machines useaccelerometers and gyroscopes individually or in combination to providecountless functionalities related to motion detection and analysis.

According to various embodiments, motion detection is performed withpressure sensors. Various embodiment pressure sensors are arrangedfacing different directions and configured to preferentially detectpressure waves in primary directions aligned with each respectivepressure sensor. In an embodiment, three pressure sensors are arrangedorthogonally and configured to preferentially sense pressures from thesurrounding medium corresponding to velocity in a specific direction.The pressure signals may be filtered and a difference signal may begenerated in order to determine the direction of motion. In variousembodiments, the pressure sensors used may be microphones, dynamicpressure sensors, or static pressure sensors. Further, the sound port orpressure port connecting the respective pressure sensor to thesurrounding medium may include a directionally preferential guide orother structure, similar to a pitot tube, for example. Each pressuresensor includes a microfabricated diaphragm or membrane arranged with aplanar surface having a normal pointing in a primary direction ofmovement for the respective sensor. Various embodiments andmodifications are described herein.

FIG. 1 illustrates a perspective view of an embodiment motion sensor 100a including three pressure sensors 102 arranged orthogonally on device104. According to various embodiments, device 104 may be any type ofdevice that incorporates motion sensing such as an automobile, a portionor an automobile, a mobile phone, a tablet computer, a computer, acomputer peripheral such as a mouse, a video game console, a video gamecontroller, sporting equipment such as a football helmet, or any otherdevice. Each pressure sensor 102 x, 102 y, 102 z is coupled to thesurrounding medium, e.g., air, through a sound port or pressure port andincludes a sensing surface arranged with a normal pointing parallel tothe x-axis, y-axis, and z-axis, respectively. When device 104 is movedalong any axis, the corresponding pressure sensor 102 x, 102 y, or 102 zsenses a pressure change while the other pressure sensors arrangedorthogonal to the motion do not sense a pressure change, or sense asmall pressure change. If device 104 is moved diagonally to any axis, aprocessing circuit may compare the generated pressure signals from eachpressure sensor 102 x, 102 y, 102 z, remove common components, anddetermine the velocity direction or velocity magnitude. In variousembodiments, the pressure change sensed during a motion is proportionalto the velocity of the motion and the fluid incident on the respectivepressure sensor. Due to changes of altitude or environmental activity,such as opening and closing of doors, for example, typically allpressure sensors experience approximately the same signal. In variousembodiments, common components may be extracted and cancelled by theprocessing circuit, which may include a signal processor.

In various embodiments, device 104 includes or is coupled to aprocessing circuit (not shown) that is coupled to each pressure sensor102. The processing circuit may include a band pass filter or a low passfilter. The three pressure sensors 102 x, 102 y, 102 z may each beidentical or each may be different. In various embodiments, pressuresensors 102 x, 102 y, 102 z are microphones or MEMS microphones, dynamicpressure sensors, or static pressure sensors. Each pressure sensor mayinclude a pitot tube or other directionally preferential structure onthe pressure port to decrease the orthogonal direction sensitivity ineach respective pressure sensor. In particular embodiments, dynamicpressure sensors are used as described in co-pending patent applicationSer. No. 14/231,068 entitled “Dynamic Pressure Sensor” and filed Mar.31, 2014, which is incorporated herein in its entirety.

In various embodiments, motion sensor 100 a includes only a singlepressure sensor 102 or only two pressure sensors 102. In someembodiments, device 104 may be a device that exhibits a reproduciblemotion. For example, device 104 may include a lever, hinged lid, such asfor a laptop computer, or other movable portion that undergoes areproducible motion. In such embodiments, a single pressure sensor 102may be affixed to device 104 and configured to detect the reproduciblemotion. The pressure sensor may be coupled to a band pass filter or alow pass filter.

FIG. 2 illustrates a waveform diagram of example motion detectionsignals in an embodiment motion sensor, such as device 104 in FIG. 1.Pressure signal 101 depicts a single measured and transduced pressuresignal as a device undergoes various movements. According to variousembodiments, as the device moves up or down, which in this casecorrespond to motions aligned with the sensor producing pressure signal101, a detectable signal peak is generated. When the device moves rightor left, which corresponds to motions orthogonal to the sensor producingpressure signal 101, little or no signal is generated. In variousembodiments, such pressure signals from multiple sensors may be used todetect movements in any direction. In some embodiments, the combinationsof pressure signals may be used to differentiate between ambientpressure changes, sounds, and motion. For example, pressure signalsdetected simultaneously at three sensors may correspond to an ambientair pressure change or sound pressure signal.

FIG. 3 illustrates a functional block diagram of an embodiment motionsensor system 110 including sensor 112, filter 114, comparison circuit116, and signal processor 118. According to various embodiments, sensor112 includes orthogonally placed pressure sensors, such as dynamicpressure sensors or MEMS microphones, for example, configured to detectpressure signals preferentially in different directions. Sensor 112generates transduced pressure signals and supplies the generatedpressure signals to filter 114 for filtering. In various embodiments,filter 114 applies a low pass filter (LPF) or a band pass filter (BPF)to the pressure signals. Filter 114 may be applied in order to filterout non-movement related pressure signals such as sound waves or ambientpressure changes. The filtered pressure signals are supplied tocomparison circuit 116 that compares the pressure signals originatingfrom different pressure sensors. For example, sensor 112 may detectmultiple pressure waves or variations, but comparison circuit 116 mayremove components of the pressure signals common to more than onepressure signal in order to isolate specific movement directions. Insome embodiments, comparison circuit 116 may include a differencecircuit that calculates a difference signal between the pressure signalsoriginating from any number of different pressure sensors. Signalprocessor 118 receives the difference signals and may perform furthercalculation to generate a motion value corresponding to velocitydirection. The motion value may also include velocity magnitude,dependent on signal processor 118. Signal processor 118 may perform acomparison or difference operation. In such embodiments, comparisoncircuit 116 may be omitted. In various other embodiments, comparisoncircuit 116 or signal processor 118 may implement further, moreadvanced, algorithms to evaluate motion information.

In various embodiments, the LPF may have a high frequency roll-offfrequency of 100 Hz, passing frequencies below 100 Hz. In moreparticular embodiments, the LPF may only pass frequencies below 10 Hz.The BPF may pass a band between 0.5 and 100 Hz, between 0.5 and 10 Hz,or between 1 and 10 Hz in some specific embodiments. Sensor 112 mayinclude multiple sensors arranged in different directions or locations,such as orthogonally or approximately orthogonally. For example, sensor112 may include two pressure sensors, three pressure sensors, or morethan three pressure sensors. In an alternative embodiment, sensor 112includes only a single pressure sensor attached to a structure.

According to various embodiments, difference circuit 116 and signalprocessor may be implemented in numerous different ways, for example,using analog or digital integrated circuits, a single microprocessor ormultiple microprocessors, an application processor, or some combinationthereof. In such embodiments, difference circuit 116 and signalprocessor 118 are not necessarily separate components, but may be fullyor partially integrated as well.

FIG. 4 illustrates a system block diagram of an embodiment motion sensorsystem 120 including three pressure sensors 102 x, 102 y, and 102 z,application specific integrated circuit (ASIC) 122, and applicationprocessor 124. According to various embodiments, motion sensor system120 implements one embodiment of motion sensor system 110. ASIC 122receives transduced pressure signals from pressure sensors 102 x, 102 y,102 z and performs initial processing. For example, ASIC 122 may amplifyand filter each signal. Additionally, ASIC 122 may calculate adifference signal based on the transduced signals. Application processor124 receives the initially processed signals from ASIC 122 and performsadditional signal processing. In some embodiments, application processor124 calculates the difference signal based on the individual pressuresignals. Application processor 124 also performs further signalprocessing in order to detect and characterize movements. For example,application processor 124 calculates a velocity vector including themagnitude and direction of detected and characterized movements.Application processor 124 may also perform numerous other calculationsand may be connected to a data bus or interface for various electronicdevices or systems.

FIG. 5 illustrates a perspective view of an embodiment pressure sensorstructure 130 including an embodiment sensor to air interface with apressure sensor 102 and a pressure port 135. According to variousembodiments, pressure port 135 may be a long sound or pressure portcoupled to a pressure sensor, such as MEMS microphone or a dynamicpressure sensor. Pressure port 135 may have a width W, or diameter, anda length L. In such embodiments, the pressure sensor 102 includes amicrofabricated deflectable diaphragm or membrane formed with a sensingstructure for detecting deflections of the membrane. The deflectablemembrane may have a planar surface with a diameter or long dimensionapproximately equal to or near the width W of pressure port 135. Invarious embodiments, length L is greater than width W. In particularembodiments, length L may be at least three times greater than width W.In one specific embodiment, length L is at least ten times greater thanwidth W.

In various embodiments, pressure port 135 is operable to allow pressurewaves to reach the membrane of pressure sensor 102 when the pressurewaves incident on the membrane are parallel to the normal of the planarsurface of the membrane. Pressure port 135 allows pressure waves to passlengthwise through the port. However, pressure port 135 is operable toblock or limit pressure waves traveling perpendicular to the normal ofthe planar surface of the membrane. Such pressure waves are limited fromentering pressure port 135 due to the angle of incidence on the opening.Pressure waves incident at a diagonal angle, neither perpendicular norparallel to the planar surface of the membrane, are partially blocked,thereby allowing a portion of the pressure wave to pass through pressureport 135.

In other embodiments, pressure port 135 may be any shape including, forexample, circular, square, or other cross sections, or even taperedand/or bent structures. Further, more detailed, explanations ofembodiment pressure sensors with similar features as pressure sensorstructure 130 are described below in reference to FIGS. 8, 9, 10 a, and10 b.

FIG. 6 illustrates a side view of another embodiment motion sensor 100 bincluding six sided device 106 and at least six pressure sensors 102.According to various embodiments, device 106 may be any type of devicethat incorporates motion sensing as described in reference to device 104in FIG. 1. Pressure sensors 102 are attached or included on each side ofdevice 106 in order to increase pressure signal detection. Device 106includes or is coupled to processing circuits for analyzing the signalsoriginating from pressure sensors 102 as described in reference to FIGS.1, 3, and 4. In such embodiments, additional signal processing may beapplied to the transduced pressure signals for comparison purposes toimprove motion detection and characterization.

FIG. 7 illustrates a side view of a further embodiment motion sensor 100c including eight sided device 108 and at least six pressure sensors102. According to various embodiments, motion sensor 100 c and device108 are similar to motion sensor 100 a and 100 b as described inreference to FIGS. 1 and 6 above. These structures are shown to beillustrative of numerous shapes and configurations of pressure sensors102 in various embodiments. A device, such as device 108, may have manysides and include pressure sensors 102 on any of the sides. Pressuresensors 102 are arranged to preferentially sense pressure waves inspecific directions. Processing circuits, such as described in referenceto FIGS. 3 and 4, use the transduced signals to detect and characterizethe corresponding movements. In various embodiments, many pressuresensors 102 may be arranged in any number different directions andcoupled to the processing circuits described in reference to FIGS. 3 and4.

FIG. 8 illustrates a cross-sectional view of an embodiment pressuresensor structure 200 a including pressure port 202, guide structure 204,sensing membrane 206, and sensing structure 208. According to variousembodiments, pressure waves enter through pressure port 202 in thedirection of membrane 206 and cause membrane 206 to deflect. Sensingstructure 208 detects and measures the deflection of membrane 206 andelectrical leads (not shown) provide transduced pressure signals frommembrane 206 and sensing structure 208 to processing circuits (notshown), such as an integrated circuit or an application processor, forexample, as described in reference to FIGS. 3 and 4. Pressure port 202may be formed as an opening in guide structure 204. Similar to theembodiments described in reference to FIG. 5, pressure port 202 andguide structure 204 guide pressure waves toward membrane 206. In variousembodiments, pressure port 202 may allow or guide pressure wavestraveling parallel, or approximately parallel, to normal 207 of thesurface of membrane 206. Conversely, pressure port 202 may limit orprevent pressure waves traveling perpendicular, or approximatelyperpendicular, to normal 207. Thus, in such embodiments, pressure port202 preferentially receives pressure waves traveling parallel to normal207 and rejects pressure waves traveling perpendicular to normal 207.

In various embodiments, pressure sensor structure 200 a is amicrofabricated device, such as a MEMS sensor. In some embodiments,pressure sensor structure 200 a is a MEMS dynamic pressure sensor or aMEMS static pressure sensor. In other embodiments, pressure sensorstructure 200 a is a MEMS microphone. According to various embodiments,membrane 206 is a deflectable membrane formed on and supported by spacer212, which is formed on sensing structure 208. Sensing structure 208 maybe a perforated backplate. Substrate 210 provides the support structurefor sensing structure 208 and membrane 206 and includes a cavity 211.

In an embodiment, substrate 210 is a silicon substrate and sensingstructure 208 and membrane 206 are doped polysilicon layers. In otherembodiments, substrate 210 may be any semiconductor material, polymer,or the like. Membrane 206 and sensing structure 208 may be formed of anyconductive material, such as metals, e.g., aluminum, or conductivecompounds, for example. Membrane 206 or sensing structure 208 may alsobe formed of multiple layers, such as a non-conductive structural layerand a conductive layer. For example, membrane 206 or sensing structure208 may be formed of an insulator or dielectric, such as an oxide ornitride, and may be coated with a metal layer, such as gold. Sensingstructure 208 and membrane 206 are formed as a parallel plate capacitorwith a separation distance that varies as membrane 206 deflects inresponse to incident pressure waves.

In various embodiments, guide structure 204 may be an attached componentor may be formed through in the microfabrication process. Guidestructure 204 is formed of a polymer and attached to the microfabricatedstructure of membrane 206, sensing structure 208, and substrate 210 inone embodiment. Guide structure 204 is formed of a device package,including plastic, metal, or a printed circuit board (PCB), for example,and the microfabricated structure is attached in another embodiment.Guide structure 204 may be any shape, such as square or circularcylinder, for example. For further details and embodiments regardingvarious materials and structures relating to a MEMS microphone or adynamic pressure sensor, refer to co-pending patent application Ser. No.14/231,068, as discussed above. Further embodiments related to pressuresensor structure 200 a are described in reference to FIGS. 9, 10 a, and10 b below. Corresponding numerals have corresponding structure anddescription of corresponding elements described in reference to FIG. 8is not repeated in reference FIGS. 9, 10 a, and 10 b.

FIG. 9 illustrates a cross-sectional view of another embodiment pressuresensor structure 200 b including pressure port 202, filed with foam 214,guide structure 204, sensing membrane 206, and sensing structure 208.According to various embodiments, foam 214 may be included in pressureport 202 in order to filter sound pressure waves entering pressure port202. Foam 214 may serve as a type of filter, removing higher frequencysignals and also reducing some movement related pressure waves. Forexample, foam 214 may reduce or limit pressure waves caused byhorizontal movements in reference to the direction of pressure port 202(i.e. may limit pressure waves from movements perpendicular to normal207). In some embodiments, foam 214 includes packaging foam or audiofoam, as is commonly available. Foam 214 may be included in a MEMSmicrophone in some embodiments and may be applied across or within thesound port of a MEMS microphone. Foam 214 may serve as an additional lowpass filter (LPF) and may be combined with a circuit implementation ofan LPF as described in reference to FIGS. 3 and 4 above. Foam 214 mayallow ambient pressure changes to be sensed. In such embodiments,additional signal processing or filtering may be performed todistinguish between motion induced pressure signals and ambient pressurechanges.

FIGS. 10 a and 10 b illustrate a cross-sectional view and a top view,respectively, of a further embodiment pressure sensor structure 200 cincluding pressure port 202, guide structure 204, sensing membrane 206,sensing structure 208, and guide grid 216 formed in guide structure 204.According to various embodiments, guide grid 216 further increases thepreferential reception of pressure waves traveling parallel to normal207 and increase the rejection of pressure waves traveling perpendicularto normal 207. FIG. 10 a shows a side view of guide grid 216 and FIG. 10b shows a top view of guide grid 216. In various embodiments, guide grid216 is a rectangular grid forming rectangular cylindrical paths tomembrane 206. In other embodiments, guide grid 216 may be configuredwith other shapes including any path to membrane 206. Further, guidegrid 216 may be formed of a polymer, metal, or semiconductor material,for example. In some embodiments, guide grid 216 is formed of the samematerial as guide structure 204.

FIG. 11 illustrates a block diagram of an embodiment method of sensingmotion 300 including steps 302-306. According to various embodiments,step 302 includes generating a pressure signal with the pressure sensor.The pressure sensor may be coupled to a structure that exhibits areproducible motion in some embodiments. The pressure signal is bandpass filtered in step 304. Step 306 includes detecting a motion based onthe filtered pressure signal. Step 306 may include detecting thereproducible motion in some embodiments. In other embodiments, furthermodifications may be applied to method 300 and the steps may beperformed in various other orders.

FIG. 12 illustrates a block diagram of another embodiment method ofsensing motion 320 including steps 322-328. According to variousembodiments, step 322 includes receiving a first signal and a secondsignal from a first pressure sensor and a second pressure. Step 324includes low pass filtering the first signal and second signal.Following step 324, step 326 includes determining a difference signalfrom the first signal and the second signal. In step 328, a motion ischaracterized based on the difference signal. In other embodiments,further modifications may be applied method 320 and the steps may beperformed in various other orders.

FIG. 13 illustrates a system block diagram of an embodiment MEMSmicrophone system 340 including MEMS microphones 342 and 344 coupled toaudio processing circuit 348 and motion processing circuit 350.According to various embodiments, MEMS microphone system 340 may beincluded in a mobile phone, tablet computer, or any other applicationswith microphones. MEMS microphones 342 and 344 receive pressure wavesfrom an ambient environment and transduce the pressure waves toelectrical signals. The electrical pressure signals are processed byaudio processing circuit 348 and motion processing circuit 350. Invarious embodiments, motion processing circuit 350 may include filteringcircuits, comparison circuits, and a signal processor for generatingmotion value 354 related to a determined motion based on pressuresignals received at MEMS microphones 342 and 344. Motion processingcircuit 350 may function and include components as described above inreference to FIGS. 3 and 4 above.

In various embodiments, audio processing circuit 348 may include afilter and other audio processing circuits commonly used for microphonesignal processing. Audio processing circuit 348 supplies audio signalsto speaker 352 or another component configured to receive audio signals.Audio processing circuit 348 may filter the electrical pressure signalsreceived from MEMS microphones 342 and 344 according to an audio band,passing frequencies between, for example, 500 Hz and 25 kHz. Similarly,motion processing circuit 350 may filter the electrical pressure signalsreceived from MEMS microphones 342 and 344 according to a motionrelevant band, passing frequencies between, for example, 0.5 Hz and 10Hz. Other frequency bands may be used for both audio processing circuit348 and motion processing circuit 350 in other embodiments.

According to various embodiments, control signal CTRL may enable ordisable audio processing circuit 348 and motion processing circuit 350.MEMS microphone system 340 may include an amplifier 346 coupled to MEMSmicrophones 342 and 344. In various embodiments, any number of MEMSmicrophones may be included, such as 1, 2, 3, or 6 for example, and eachmay be coupled to an amplifier. In some embodiments, amplifiers, MEMSmicrophones, or processing circuits, such as low pass or band passfilters, may be included on a single integrated circuit (IC) or multipleICs. MEMS microphone system 340 may include any number of ICs orprocessors.

According to an embodiment, a method of sensing motion includesreceiving a first signal from a first pressure sensor and a secondsignal from a second pressure sensor, comparing the first signal and thesecond signal, and characterizing a motion based on the comparing.

In various embodiments, the method of sensing motion further includeslow pass filtering the first signal and second signal. Low passfiltering may include passing frequencies below 10 Hz. In someembodiments, the method includes receiving a third signal from a thirdpressure sensor and comparing the first signal, second signal, and thirdsignal. Comparing the first signal and the second signal may includedetermining a difference signal between the first signal and the secondsignal.

In various embodiments, the method of sensing motion further includesgenerating the first signal at a first deflectable membrane and a firstsensing structure formed adjacent the first deflectable membrane andgenerating the second signal at a second deflectable membrane and asecond sensing structure formed adjacent the second deflectablemembrane. The method may also include receiving pressure waves in afirst pressure port coupled to the first membrane and having a lengthextending away from the first membrane at least three times greater thana longest dimension of the first membrane. The method may furtherinclude receiving pressure waves in a second pressure port coupled tothe second membrane and having a length extending away from the secondmembrane at least three times greater than a longest dimension of thesecond membrane.

According to an embodiment, a motion sensor includes a plurality ofpressure sensors and a motion detection circuit coupled to the pluralityof pressure sensors. Each of the plurality of pressure sensors includesa membrane having a planar surface with a normal pointing in a differentdirection and the plurality of pressure sensors are configured togenerate pressure signals based on deflections of each membrane. Themotion detection circuit is configured to receive the pressure signalsfrom the plurality of pressure sensors, compare the pressure signals toeach other, and characterize a motion based on comparing the pressuresignals to each other.

In various embodiments, the motion detection circuit includes a low passfilter configured to low pass filter the pressure signals beforecomparing the pressure signals to each other. The low pass filter may beconfigured to pass frequencies below 10 Hz. The plurality of pressuresensors may include two pressure sensors. The plurality of pressuresensors may include three pressure sensors. In some embodiments eachpressure sensor of the plurality of pressure sensors includes a soundport having a first length in a direction parallel to the respectivenormal at least three times longer than a longest dimension of therespective membrane. At least one sound port may be filled with foam. Atleast one sound port may include a guide grid. The first length of atleast one sound port may be at least ten times longer than a longestdimension of the respective membrane.

In various embodiments, each normal of the plurality of pressure sensorsis orthogonal to each other normal of the plurality of pressure sensors.Each pressure sensor of the plurality of pressure sensors may be one ofa group consisting of a static pressure sensor, a dynamic pressuresensor, and a microelectromechanical (MEMS) microphone.

According to an embodiment, a method of sensing motion includesgenerating a pressure signal with a pressure sensor, band pass filteringthe pressure signal, and detecting a motion based on the filteredpressure signal. Band pass filtering includes passing a frequency bandbetween 0.5 Hz and 50 Hz.

In various embodiments, band pass filtering includes passing a frequencyband only between 0.5 Hz and 10 Hz. The pressure sensor may be coupledto a structure that exhibits a reproducible motion and detecting themotion may include detecting the reproducible motion. The pressuresensor may include a deflectable membrane formed adjacent to a sensingstructure and configured to generate the pressure signal in response todeflections of the deflectable membrane. In some embodiments, thepressure sensor includes a pressure port coupled to the deflectablemembrane. The pressure port has a length extending away from themembrane that is at least three times greater than a longest dimensionof the membrane.

According to an embodiment, a microphone system includes a plurality ofmicroelectromechanical system (MEMS) microphones including a pluralityof signal outputs, a motion processing circuit coupled to the pluralityof signal outputs, and an audio processing circuit coupled to theplurality of signal outputs. The signal outputs are configured to supplya plurality of pressure signals generated by the plurality of MEMSmicrophones. The motion processing circuit is configured to characterizemotions of the microphone system based on the plurality of pressuresignals. The audio processing circuit is configured to output anelectrical audio signal based on the plurality of pressure signals.

In various embodiments, the motion processing circuit includes a lowpass filter configured to pass frequencies below 10 Hz. The audioprocessing circuit may include a high pass filter configured to passfrequencies above 500 Hz. In some embodiments, the plurality of MEMSmicrophones includes only two MEMS microphones.

According to various embodiments described herein, advantages mayinclude motion detection using pressure sensors or microphones, motiondetection with decreased system cost, and measurement of velocity of adevice based on measured pressure waves. In embodiments includingmicrophone systems, such as cellular phones or tablets for example,advantages may include using multiple existing microphones that may bereconfigured to support both microphone functionality and motion sensorfunctionality without additional sound ports or pressure ports.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. A method of sensing motion comprising: receiving a first signal from a first pressure sensor and a second signal from a second pressure sensor; comparing the first signal and the second signal; and characterizing a motion based on the comparing.
 2. The method of claim 1, further comprising low pass filtering the first signal and second signal.
 3. The method of claim 2, wherein low pass filtering comprises passing frequencies below 10 Hz.
 4. The method of claim 1, further comprising: receiving a third signal from a third pressure sensor; and comparing the first signal, second signal, and third signal.
 5. The method of claim 1, wherein comparing the first signal and the second signal comprises determining a difference signal between the first signal and the second signal.
 6. The method of claim 1, further comprising: generating the first signal at a first deflectable membrane and a first sensing structure formed adjacent the first deflectable membrane; and generating the second signal at a second deflectable membrane and a second sensing structure formed adjacent the second deflectable membrane.
 7. The method of claim 6, further comprising: receiving pressure waves in a first pressure port coupled to the first membrane and having a length extending away from the first membrane at least three times greater than a longest dimension of the first membrane; and receiving pressure waves in a second pressure port coupled to the second membrane and having a length extending away from the second membrane at least three times greater than a longest dimension of the second membrane.
 8. A motion sensor comprising: a plurality of pressure sensors, each comprising a membrane having a planar surface with a normal pointing in a different direction, wherein the plurality of pressure sensors are configured to generate pressure signals based on deflections of each membrane; and a motion detection circuit coupled to the plurality of pressure sensors, wherein the motion detection circuit is configured to: receive the pressure signals from the plurality of pressure sensors, compare the pressure signals to each other, and characterize a motion based on comparing the pressure signals to each other.
 9. The motion sensor of claim 8, wherein the motion detection circuit further comprises a low pass filter configured to low pass filter the pressure signals before comparing the pressure signals to each other.
 10. The motion sensor of claim 9, wherein the low pass filter is configured to pass frequencies below 10 Hz.
 11. The motion sensor of claim 8, wherein the plurality of pressure sensors comprises two pressure sensors.
 12. The motion sensor of claim 8, wherein the plurality of pressure sensors comprises three pressure sensors.
 13. The motion sensor of claim 8, wherein each pressure sensor of the plurality of pressure sensors comprises a sound port having a first length in a direction parallel to the respective normal at least three times longer than a longest dimension of the respective membrane.
 14. The motion sensor of claim 13, wherein at least one sound port is filled with foam.
 15. The motion sensor of claim 13, wherein at least one sound port comprises a guide grid.
 16. The motion sensor of claim 13, wherein the first length of at least one sound port is at least ten times longer than a longest dimension of the respective membrane.
 17. The motion sensor of claim 8, wherein each normal of the plurality of pressure sensors is orthogonal to each other normal of the plurality of pressure sensors.
 18. The motion sensor of claim 8, wherein each pressure sensor of the plurality of pressure sensors comprises one of a group consisting of a static pressure sensor, a dynamic pressure sensor, and a microelectromechanical (MEMS) microphone.
 19. A method of sensing motion comprising: generating a pressure signal with a pressure sensor; band pass filtering the pressure signal, wherein band pass filtering passes a frequency band between 0.5 Hz and 50 Hz; and detecting a motion based on the filtered pressure signal.
 20. The method of claim 19, wherein band pass filtering comprises passing a frequency band between 0.5 Hz and 10 Hz.
 21. The method of claim 19, wherein the pressure sensor is coupled to a structure that exhibits a reproducible motion and detecting the motion comprises detecting the reproducible motion.
 22. The method of claim 19, wherein the pressure sensor comprises a deflectable membrane formed adjacent to a sensing structure and configured to generate the pressure signal in response to deflections of the deflectable membrane.
 23. The method of claim 22, wherein the pressure sensor further comprises a pressure port coupled to the deflectable membrane, wherein the pressure port has a length extending away from the membrane that is at least three times greater than a longest dimension of the membrane.
 24. A microphone system comprising: a plurality of microelectromechanical system (MEMS) microphones comprising a plurality of signal outputs, wherein the signal outputs are configured to supply a plurality of pressure signals generated by the plurality of MEMS microphones; a motion processing circuit coupled to the plurality of signal outputs, wherein the motion processing circuit is configured to characterize motions of the microphone system based on the plurality of pressure signals; and an audio processing circuit coupled to the plurality of signal outputs, wherein the audio processing circuit is configured to output an electrical audio signal based on the plurality of pressure signals.
 25. The microphone system of claim 24, wherein the motion processing circuit comprises a low pass filter configured to pass frequencies below 10 Hz.
 26. The microphone system of claim 25, wherein the audio processing circuit comprises a high pass filter configured to pass frequencies above 500 Hz.
 27. The microphone system of claim 24, wherein the plurality of MEMS microphones comprises two MEMS microphones. 